I. Field of the Invention
The present invention relates to roadway reflectors, and more particularly, to roadway reflectors of the type adapted to be mounted on a roadway to reflect light from the headlight of an oncoming automotive vehicle and thereby delineate the traffic lanes of the road to the driver of the vehicle.
II. Description of the Prior Art
Reflective roadway markers are used by highway departments and by others for delineating highway lines (such as traffic lanes) on pavement. Properly designed reflective markers are clearly visible at night by reflecting light from an oncoming vehicle back to the vehicle. Such markers generally include a body and some sort of a reflective lens supported by the body.
U.S. Pat. No. 3,409,344 (Balint et al, Nov. 5, 1968) discloses a roadway marker including a housing molded in situ about a plurality of reflective inserts, the inserts having substantially flat outer surfaces and a plurality of retro-reflective prisms on their inner surfaces. The inner surfaces of the prisms are coated with a metalized layer, and the entire housing is filled with a plastic material in order to provide strength and rigidity to the marker.
U.S. Pat. No. 3,332,327 (Heenan, July 25, 1967) discloses a similar pavement marker adapted to be placed on highways. The pavement marker has a front face inclined at a predetermined angle with respect to the roadway surface, so that a self-cleaning effect is provided by virtue of the predetermined angle. The angle that the reflective lens makes in relation to the pavement surface affects the relative efficiency of the retro-reflective prism surfaces; it is generally desired to select the angle so that the reflective efficiency of the prism surface is maximized.
U.S. Pat. No. 4,340,319 (Johnson et al) and U.S. Pat. No. 3,332,327 each disclose that mechanical abrasion of the front face of the lens portion of a pavement marker decreases when the angle of the front face increases. As that angle increases, however, the cleaning action obtained by tire wiping on the front face of the lens decreases. For reflective lenses including orthogonal (cubic corner) retroreflective prisms, satisfactory optical effectiveness is obtained when the angle of the front face of the lens member is disposed between 15 and 45 degrees to the horizontal, and most preferably at about 30 degrees to the horizontal.
U.S. Pat. No. 4,340,319 also notes that the problem of abrasion becomes particularly acute when pavement markers are used in areas where abrasive materials such as salt are distributed over the roadway surface during winter months. Typically, such pavement markers will include soft plastic lenses having fine optical quality. Unfortunately, such lenses are highly susceptible to abrasion. It has been found in use that sand and salt are continually brought into contact with the lenses from the wiping action of the vehicle tires. The combination of such abrasive materials and the wiping action of them tends to scratch and grind the front face of the lens and diminish the optical effectiveness and reflective quality of the pavement marker.
U.S. Pat. No. 4,340,319 attempts to solve this problem by providing a layer of untempered glass sheet disposed under tension on the light receiving and refracting portion of the lens. Glass was utilized because other possible coatings for the lens either were known to be unable to provide adequate abrasion resistance, or required curing temperatures which were so high that the temperatures distorted the plastic material of the reflector, thereby deteriorating the reflector optics seriously. In at least one figure, the glass face is shown most deeply recessed at its lowermost edge. The brow which retains the glass face in position under tension appears to be formed smoothly and continuously with the top and lateral faces of the marker, and appears not to extend or protrude above those faces.
A marker believed to incorporate the invention claimed in U.S. Pat. No. 4,340,319 is sold by Stimsonite Products, Amerace Corporation, Niles, Illinois, under the name "Stimsonite 948 Reflective Pavement Marker." The marker is described as including a glass face recessed within the shell of the marker. The glass face is untempered and is held in place under tension by and beneath an extended brow. The asserted purpose for recessing the glass face is to reduce top edge deterioration. The marker is sold for use in climates where snowplowing does not occur.
The pavement marker disclosed in U.S. Pat. No. 4,753,548 (Forrer, June 28, 1988) solved these and other problems by providing a photopolymerizable acrylic resin composition as a hard coat on the front surface of the retro-reflective lens in such pavement markers. When polymerized, the clear acrylic hard coat provided a resistance to abrasion superior to the abrasion resistance of the soft plastic lens, while it simultaneously avoided both the expense and potential for separation of a multipiece construction such as that shown in U.S. Pat. No. 4,340,319 and any distortion of the plastic material of the reflector encountered with thermocuring resins. Indeed, the top coat of acrylic in U.S. Pat. No. 4,753,548 was preferably formed integrally with and in situ upon the front surface of the lens.
This prior art construction is more particularly shown in FIGS. 1 and 2. A pavement marker constructed in accordance with U.S. Pat. No. 4,753,548 is generally shown at 10. The pavement marker 10 includes a housing 12 having a lower base portion 14 which is adapted to be adhered to a roadway surface 16. The housing 12 is hollow and includes one or more side walls 18 extending substantially upwardly from the base portion 14.
A retro-reflective lens 20 is mounted on at least one of the walls 18. The lens 20 has a front surface 22 facing outwardly from the wall 18. An abrasion resistant photopolymerizable acrylic protective hard coat 24 is deposited over the lens 20 for resisting abrasion of the lens 20 and reducing the loss of optical efficiency resulting from abrasion. The protective hard coat 24 is chemically adhered to and formed integral with the front surface 22 of the lens 20. The lens 20 also includes a rear face 26 having a plurality of reflex-reflector prisms 28 on at least a portion of the rear face 26. The lens 20 is received in a recess 30 in the wall 18. The hollow interior of the housing 12 is filled with a suitable filler 32, such as sand bound with an aggregating agent, adhereable to both the interior surface of the housing 12 and the rear surface 26 of the lens 20.
Again, the specific method of constructing such a pavement marker and the functions of each of its particular elements are discussed in more detail in U.S. Pat. No. 4,753,548 and U.S. Pat. No. 3,409,344, the disclosures of which are incorporated by reference herein.
In use, as shown in FIG. 2, the pavement marker 10 is adhered to the roadway surface 16 on which a vehicle including a vehicle tire 34 rides. When the marker 10 is impacted by the tire 34, such as when the driver of the vehicle changes traffic lanes, the tire 34 moves from its first position shown in solid line in FIG. 2 to its position shown in phantom in FIG. 2, abutting the marker wall 18 and abraiding the hard acrylic coating 24 on the lens 22. The force of impact is particularly acute at the upper edge 36 of the wall 18. Repeated impacts from vehicle tires, particularly under conditions where there is salt or sand on the road, result in the greatest likelihood of wear and/or peeling of the coating 24 at its top edge 38. Such abrasive wear or peeling would obviate the advantages intended to be achieved by the use of the abrasion resistant hard coat 24.